A couple quick, but significant comments:
1. For manageability (especially when testing), spec should be broken down into
more subsections than it is currently. Except where pairs of properties are
defined together (e.g. 'cue-before' + 'cue-after' share a definition), each
property should get its own subsection.
2. It would be good for each feature that corresponds to an SSML feature to
link to the appropriate section of the SSML spec, perhaps in a note, so that
it's well understood how CSS3 Speech and SSML correspond. This should also
help reviewers catch any mismatches. :)
~fantasai